Electrodeposition of metals



Nov. 2o, 1934. y R, H, ATKINSON 1,981,715

ELECTRODEPOS ITION OF METALS VFiled July 9, 1932 IN V EN TOR.

A TTORNEYS.

Patented Nov. 20, 1934 l i l -uNl'lllD STATES PATENT critici?.v

Emcrnonnposlriolv or METALS Ralph Hall Atkinson, Acton, England.`assignor to The International Nickel Company, Inc., New York, N. Y., acorporation of Delaware Application July 9, 1932, Serial No. 621,619 InGreat Britain July 11, 1931 3 Claims. (Cl. 204-1) This invention relatesprimarily to electroplatin a non-diaphragm cell, but which in a diaingand the electro-deposition of metals and alphragmv cell, according tothe invention', is formed lOyso only in the anolyte where itsaccumulation does It is an object of the invention to provide a bath notaiect the plating process because part of the 'Iwhich shall have a longlife without the use of anolyte can be evacuated periodically. The pal-30 a soluble anode'. ladium on the other hand, being wholly cationic,Other objects and advantages will become apmigruttes to the cathode andthus can easily be parent from the following description. kept-withinthe catholyte compartment. How- The invention consists essentially inthe use of ever, the invention is not dependent on the acan insolubleanode in a diaphragm cell with an curacy of the above theory.

ammoniacal anolyte substantiallyfree from any The evacuation of part ofthe anolyte can be metal compound arid with a catholyte which comeiectedin any convenient way either continuousprises an ammoniacal solution ofa compound or, ly or peliOdiCa-lly- The anOlyte removed may be compoundsof a, metal or metals and which is replaced either by water or byammonia solution. l5 capable of yielding electro-deposits. In carryingout the process with palladosam- 70 The conunercial development ofammoniacal mine Chloride the Catholyte may Conveniently 00nelectrolyteshas not received much attention besist 0f an aqueOus sOluifiOneOntaiIiiIig about 5 cause previously baths of thistype lcould lhavegrams of free ammonia and about grams of only a short life on account ofthe fact that most palladium per liter. The anOlyte may cOnSiStOf 20metal anodes are insoluble in these electrolytes, an aqueous solution ofammonia containing for 76 with the consequence that 'the meta1content-,0f example about 30 grams of ammonia ,per liter. the latter hadto be maintained 'by periodical ad- Initially al COIidUCtin salt may beadded t0 the `ditidns of salts thereby leading to undesirable anolyte,but the ammonium chloride formed duraccumulation of acid radicals' inthe plating soins operation is suiiicient to maintain the conn lution,so that although in certain cases the presduCliiVW 1n Order t0, Preventthe formation' 0f 3 ence of the diaphragm may not affect the naturenitrogen trichloride which is very explosive, strong 0f the deposit, e.g. copper and nickel, it has ammonia (specinc gravity 0.880) should beadded the advantage that it enables the electrolyte, suitat intervalstothe anolyte.v

ably replenished from time to time, to be used for In practice it isfound that goed deposits may a very much longer time than would bepossible be obtained Withatholytes containing as much 85 without adiaphragm. as about 30 grams per liter ammonium chloride. The inventionis particularly applicable to pal- Any tendency of the concentration toincrease too ladium and alloys thereof, although it ls ln no `much maybe remedied by increasing the rate way limited to these. It is,therefore, most con-` 0f evacuation 0f the aIiOlyte. venient nrst todescribe the application of. the ln- A system by means of which thecatholyte may 90 vention to the deposition or palladium and then befortified without interruption of the process to indicate some furtherapplications. is illustrated'by way of exampleinthe accompanyi It isknown to use for= plating purposes a S0111- ing drawing. In this drawingthe reference chartion of palladosammine chloride (dichiaro-dialnacier lrepresents the aIlOlYte Chamber. 2 the 40 minopalladium) v`in ammonia inan ordinary elec- Cathelyte chamber, arid 3 the diaphragm. The 95ftrolytlc cell, but although the inltlaldeposlts catholyte iscontinuously drawn on by ineens of a may be good the deposits areunsatisfactory after Siphon 4 which Serves t0 maintain the level f a.short time. In proceeding in accordance with the liquid in the cathulvtechambei- The Siphon the present invention, however,- the catholytedelivers to a vessel 5 in which'palladosammine consists of a solutionin'amnionia of apalladiumchloride is dissolved. The solution passes to aammino compound such as palladosammine chlofilter 6 and is then pumpedto a feed vessel 'I and ride. The deposits produced are ythen found tosupplies the catholyte chamber 2. The catholyte be consistently good.l gmay also be agitated in the actual plating cell The improved results arebelieved to be main. as well as continuously simulated. i. 5o 1y due tothe fact that when the palladiumP tet- The deposits of palladiumobtained by this 105 'l rammine cation, which is present in anammoniprocessV are bright up to a thickness of aboutacal solution ofpalladosammine chloride, decom- 0.00002 inch, but thicker deposits aresomewhat poses into palladium and ammonia, the latter milky.- althoughthey t adherent and suitableA `reacts at the anode with chlorine to formam: for buillng or other g operations. monium chloride which accumulatesundeslrably The current density required to give the best n0 resultsvaries with the other conditions, including the concentration of themetal salts and the temperature. As an example in palladium plating witha bath containing 15 grams of palladium per liter as tetrammine chloridethe most suitable current densities at the specified temperatures wereas follows:-

Temperature of Current density catholyte amps. per dm I 3 C. 0. l to 0.5 20 C. 0. 5 to l. 0 40 C. l. 0 to 1.5 70 C. 2. 0

' trite, uoride, acetate, tartrate, and citrate, may

with ammonium sulphate to fo be dissolved in ammonia to form catholyteswhich give good adherent deposits. Inv the case of the chloride,ammonium pallado-chloride (NH4) 2PdCl4 dissolved in aqueous ammoniayields the same electrolyte. Again, palladium may be deposited at about50 C. from ammoniacal solu' tions of palladosammine oxalate. Ammoniacalsolutions of diammino-dihydroxo-palladium or tetrammino-palladoushydroxide give particularly bright deposits. l

As an exampleof the use of tetrammine-palladous hydroxide the followingmay be given:-

A catholyte containing about 20 grams palladium and about 5 grams freeNH3, both per liter, is prepared by adding excess-of ammonia. to anaqueous solution of dihydroxo-diammino-palladium made .by a known methodand is allowed to stand for twelve hours. The anolyte contains 20 gramsammonium sulphate and 100 cc. ammonia solution (specific gravity .880)per liter. Gelatin about .05 gram per liter is added to the catholyte.The ordinary porous pot diaphragm is used. At room temperature, 2 volts,and a current density of 0.3 amp. per dm. bright adherent deposits (upto .0001 inch thick) are obtained with a current emciency of 94-97%.

As tetrammino-palladous hydroxide reacts rnistetramminopalladoussulphate, there isa tendency for the bath to lose its special characterconsequent on the diiusion of ammonium sulphate into the catholyte.removed from the cell and stored in another vessel when plating is notin progress.

Such separate storing of the catholyte may advantageously be adopted inall cases, but is especially desirable in the case oftetramminopalladous hydroxide.

The palladium ammino compounds may also be formed by using organicamines such as pyridine and ethylenediamine instead of ammonia. Thus, anaqueous solution of palladium chloride and excess of pyridine may beused as the catholyte in conjunction with an aqueous solution ofpyridine hydrochloride as the anolyte. vAgain, an aqueous solution ofpalladium chloride and excess o! ethylenediamine hydrate may be used asthe catholyte and an aqueous solution of ammonia and ammonium chlorideat' the anolyte.

Therefore the catholyte should be The -invention may be appliedadvantageously to certain other metals capable of forming metalamminessoluble in aqueous ammonia and capable of yielding eiectrodeposits,namely rhodium, platinum, iridium, nickel, copper, silver, zinc, cadmiumand cobalt. As is well known iron is not precipitated from solutions ofits salts in the presence of tartrates and citrates and such solutionsmay be used for the electro-deposition of iron. The ammoniacal solutionsmay also be used as catholytes in this invention. Tin may also bedeposited from ammoniacal catholytes containing tin chloride andammonium tartrate. Furthermore, the invention may also be used forplating with or depositing alloys of the said met- Ag2SO4, ZI1S04,CdSO4, NiSO4, COSOQ,

RhCLa, CuSO4 and Cu(NO3)1.

Platinum and iridium salts which may be used are :l

The rhodium, platinum and iridium baths should be maintainedat about C.during thev process in order to improve the current eiiiciency but .thebaths of the other metals may be worked eith'er hot or cold.

Thus, as an example of the deposition of rhodium the following may begiven: A solution containing about 7 grams rhodium as chloride andIabout 16 grams of urea per liter is boiled until a test portion givesno precipitate on adding excess of ammonia. During the boiling it may befound necessary to add a little hydrochloric acid to remove turbidity.Finally, excess of strong ammonia solution (specific gravity .880) isadded after which xthe solution is boiled. 'I'he anolyte contains 150cc. oi' strong ammonia solution (specic gravity .880) and about 25 gramsammonium chloride per liter. At '10 C., 2 volts, and a current densityof 0.3 amp. per dm2 this bath gives `bright adherent deposits of rhodiumwith a current emciency of 10%.

As an example of thedeposition of iron the following may be mentioned:about 120 grams of ferrous ammonium sulphate crystals and about -80grams of citric acid are dissolved in about 800 cc. water. After boilingand iiltering, the nltrate is allowed to cool and then made ammoniacalby adding about 120 cc. of strong ammonia solution (specific gravity.880); about 33 grams of ammonium sulphate are added and the volume madeupto 1 liter. The anolyte contains about 40 grams ammonium sulphate andabout 80 cc. of strong ammonia solution (,specinc gravity 0.880) perliter. l

At 60 C., 1.9 volts, a current density of 0.6 amp. per dm and a platingtime of 30 minutes va hard adherent deposit of iron is obtained oncopper with a current eillciency of 30% As an example of the depositionof copper the following may be mentioned: A catholyte istaken containingabout 12.5 grams per liter of copper as nitrate, about 20 grams perliter of ammonium nitrate, and a small excess of ammonia solution.

' Ihe anolyte contains about 50 grams o! ammonium nitrate and 160 cc. ofstrong ammoni solution per liter.

- At room temperature, 3.1v volts, a current density of 1 amp. per dm2and a plating time of 30, minutes, an adherent deposit 4of copper isobtained on an aluminium cathode with a current eiiiciency of 64%.

In the case of copper the presence of ammonium salts is essential forsatisfactory deposition.

As an example of the deposition of an alloy containing 90% palladium and10% cobalt the following may be mentioned: A solution containing about50 grams of cobalt sulphate crystals per liter and about grams ammoniumsulphate per liter is made ammoniacal and boiled with the addition ofhydrogen peroxide for one hour. rllhe solution is next cooled andltered, and theA ltrate mixed with an ammoniacal solution oftetrammino-palladous sulphate. The mixed s0- lution containing about14.4 grams palladium, about 1.4 grams cobalt, and about 3.4 gramsammonia, all per liter, is used as the catholyte with an anolytecontaining about 40 grams ammonium sulphate and 120 cc. of ammoniasolution (specic gravity .880) per liter. At room temperature, 3 volts,a current density vof 1 amp. per

a precipitate on making the solution ammoniacal. This solution is mixedwith an ammoniacal solution of nickel sulphate to give a catholytecontaining about 11 grams of iron, about 6 grams of nickel, about 40grams of tartaric acid and 11 grams of free NH3 per liter. About 20grams of ammonium sulphate per liter is added as conducting salt. Theanolyte contains about 50 tion of 1% of ethylenediamine hydrate renders.

palladium deposits less milky, while urea serves to increase the currentefiiciency in the deposition of rhodium. Again, the addition of a small-quantity of gelatin, of the order ot about 0.05

gram per liter,` to a tetrammino-palladous hydroxide catholyte givesbright line-grained plates.

" porous hard rubber are both' suitable.

The preferred diaphragm consists of a porous pot of the same porosityand material as those used in Leclanch cells, but of course other porou:materials may be used provided they are notattacked by the electrolyte,e. g. alundum and 'I'he cliaphragm may consists of a porous potsurrounding either the anode or thev cathode or it may be a porouspartition- (or partitions) separating the anolyte from the catholytecompartment (or compartments) v The anode may consists for example oflead, platinum, palladium or graphite'.

' The selection of the cathode metal will be determined yby the metalwhich is to be deposited upon it. When used as the cathode for palladiumplatingcopper, silver, palladium, lead, tin, nickel-silver", brass andpewter among others, all lead to the formation of good adherent depositsand other metals such as nickel and iron may be plated after preliminaryplating or coating with other metals such 'as copper and tin. Inaddition to the usual cathode metals used for electro-deposition it hasbeen found that aluminium can be plated satisfactorily with copper,possibly because an ammoniacal electrolyte has less tendency to attackaluminium than the acid or alkaline electrolytes used in other platingprocesses.

Generally the cathodes will be stationary but moving cathodes may alsobe used in suitable cases.

A'smentioned above, the invention is applicable to the electrolyticreduction of metals from their f 'si salts, such for example as theelectrolytic recovery of silver from silver chloride or of palladiumfrom palladosammine chloride. In such a case, of course, a cathode ispreferably used from which the deposit may be easily stripped. For

example, a carbon cathode may be used yfor silver, while in particularcases metal cathodes on'which only aky deposits are obtained in platingmay advantageously be used in the reduction ot metal salts.

1. A process for the electrodeposition of a metal or alloy whichcomprises establishing a porous pot diaphragm cell containing anammoniacal anolyte substantially free from a metal compound, aninsoluble anode, and a catholytev containing an ammoniacal solution of ametal to be electro-deposited; making an article to be plated a cathodein said cell; and,` passing a current through said cell to cause theelectro# deposition `on said article `oi? metal from said ammoniacalcatholyte.

2. A process for the electrodeposition of palladium which comprisesestablishing a porous pot diaphragm cell containing an anolyte of thegroup consisting of ammonia, organic amine and the like, an insolubleanode and a catholyte containing anA ammoniacal solution of a palladiumammino compound; making a'n article to be plated a cathode in said cell;and passing a cur-v rent through said cell to cause theelectrodeposition in said article of palladium from said ammoniacalcatholyte.

3. A process for the lelectrodeposition of palladium which comprisesestablishing a porous pot diaphragm cell containing an anolyte of thegroup consisting of ammonia, organic amine and the like, an insolubleanode and a catholyte containing an ammoniacal solution of palladosamf.

mine chloride; making an article to be plated a cathode in said cell;and passing a current e through said cell to cause the electrodeposltion

